1. Field of the Invention
The present invention relates to a method for producing a halogen-substituted aromatic aldehyde, particularly p-fluorobenzaldehyde and a halogen-substituted aromatic aldehyde simultaneously having a halogen atom and a hydrocarbon group each being bonded directly to the aromatic ring, which is useful as raw materials for dyes, perfumes, medicines, agricultural chemicals, and additives for resins.
2. Description of the Prior Art
The production method of aromatic aldehydes by the formylation of aromatic hydrocarbons with carbon monoxide in the presence of a catalyst such as hydrogen chloride-aluminum chloride has been well known as Gattermann Koch reaction. This reaction, however, proceeds smoothly only when the aromatic hydrocarbon is substituted by an electron donating group such as alkyl group, but, proceeds slowly when the aromatic hydrocarbon is substituted by an electron attracting group to make the industrial use thereof difficult.
For example, U.S. Pat. No. 6,300,525 B1 discloses that p-fluorobenzaldehyde is produced by the reaction of fluorobenzene with carbon monoxide in the presence of a catalyst system comprising aluminum chloride and a very small amount of hydrogen chloride. However, even after 18 h of the reaction, the yield of p-fluorobenzaldehyde is as extremely low as about 24.1% on the basis of the aluminum chloride catalyst used, and as extremely low as 3.4% on the basis of the starting fluorobenzene (Example 4). The document teaches that the reaction can be promoted by 4-methylanisole. However, even after 89 h of the reaction in the presence of 4-methylanisole, the reported yield is 64.3% on the basis of the molar amount of aluminum chloride after subtracting the molar amount of 4-methylanisole added (probably because 4-methylanisole and aluminum chloride form a 1:1 complex), 29.7% on the basis of the molar amount of aluminum chloride when not subtracting the molar amount of 4-methylanisole, and 9.4% on the basis of the starting fluorobenzene. Since U.S. Pat. No. 6,300,525 B1 is silent as to by-products in the descriptions of examples, the types and the amounts of by-products produced are unknown.
U.S. Pat. No. 6,455,739 B1 discloses that p-fluorobenzaldehyde is produced by the reaction of fluorobenzene with carbon monoxide at 45 to 100° C. in the presence of an aluminum chloride-hydrogen chloride catalyst system. Although the document does not provide the numerical yield of p-fluorobenzaldehyde, it can read from FIG. 5 as about 74% yield on the basis of aluminum chloride, and about 58% conversion, about 91.1% selectivity and about 53% yield on the basis of fluorobenzene in case of an initial load of aluminum chloride and fluorobenzene of 50:50 which is taught to be preferred. U.S. Pat. No. 6,455,739 B1 teaches that o-fluorobenzaldehyde, m-fluorobenzaldehyde, chlorobis(fluorophenyl)methane and oligomers are by-produced and the production ratio of three fluorobenzaldehyde isomers is o-isormer:m-isomer:p-isomer=1.8:0.2:98.3.
Alternatively to Gattermann Koch reaction, U.S. Pat. No. 5,068,450 discloses to produce p-fluorobenzaldehyde by the reaction of fluorobenzene with methyl formate in the presence of a hydrogen fluoride/boron trifluoride catalyst. However, since the by-production of methanol is expected in the proposed method, there is a problem of difficult separation of the by-produced methanol from hydrogen fluoride and boron trifluoride.
U.S. Pat. No. 4,588,844 discloses that p-fluorobenzaldehyde is produced by the reaction of urotropin with fluorobenzene in the presence of hydrogen fluoride. In the proposed reaction, however, a considerable amount of o-fluorobenzaldehyde is by-produced and the total yield of o- and p-fluorobenzaldehydes is as extremely low as about 30%.
U.S. Pat. No. 6,300,525 B1 mentioned above further discloses that 2-fulorotoluene, 3-fluorotoluene, etc. are converted into corresponding aldehydes by the reaction with carbon monoxide in the presence of a catalyst system comprising aluminum chloride and a very small amount of hydrogen chloride. The document teaches in the working example that 2-fluorotoluene is converted into 4-fluoro-3-methylbenzene by the reaction with carbon monoxide at 60° C. for 20 h in a yield of about 67.4% on the basis of aluminum chloride used. The calculated yield on the basis of the starting 2-fluorobenzene is only about 11%.
Thus, in known methods, the halogen-substituted aromatic aldehydes are produced only in low yields despite a long reaction time, resulting in a low production efficiency and increasing production costs. In the reaction using the hydrogen chloride-aluminum chloride catalyst system, the reaction product mixture is usually treated with water after the formylation to separate the products and the catalyst, this making the regeneration of catalyst extremely difficult. Since a large amount of waste materials is produced by hydrolysis, the disposal thereof is quite costly.